SQL SERVER – Merge Operations – Insert, Update, Delete in Single Execution

Hi, MERGE is a new feature that provides an efficient way to do multiple DML operations. In earlier versions of SQL Server, we had to write separate statements to INSERT, UPDATE, or DELETE data based on certain conditions; however, at present, by using the MERGE statement, we can include the logic of such data changes in one statement that even checks when the data is matched and then just update it, and similarly, when the data is unmatched, it is inserted.
One of the most important advantages of MERGE statement is that the entire data are read and processed only once. In earlier versions, three different statements had to be written to process three different activities (INSERT, UPDATE or DELETE); however, by using MERGE statement, all the update activities can be done in one pass of database table.
See the below blog for more info.Nice article from Dave.
http://blog.sqlauthority.com/2010/06/08/sql-server-merge-operations-insert-update-delete-in-single-execution/